In this article we report on an experimental study of the polarization of atoms in magnetized plasma (PAMP) in ${}^3\mathrm{He}$ gas under various conditions of radio-frequency (rf) excitation of plasma. Among parameters influencing the plasma dynamics are frequency, average and peak rf powers. Our data strongly indicate a significant influence of electron density in the plasma on the polarization value and buildup rate. In particular, it was found that polarization scales as $U^{\beta }$, where $U$ is the voltage across the coil in the tank circuit generating the plasma and $\beta$ is in the range of 1.3–1.5, similar to what is expected for the electron density. Experiments with the modulation of rf power show that the peak rf power governs the polarization rather than the average power. An unexpected increase in polarization related to the appearance of a small amount of impurities in the ${}^3\mathrm{He}$ gas at room temperature is found. Strong correlations between polarization and amount of oxygen impurity, which is desorbed as the temperature rises, support the hypothesis that polarization is proportional to electron density because it is expected that electron density linearly increases with impurity concentration. It was also found that the polarization and buildup rate are proportional to each other, a behavior that is common for all rf plasma frequencies. We propose a scenario that can explain the experimental observations: The polarization is limited by nuclear magnetic relaxation, while the growth rate associated with the intrinsic polarization process depends quadratically on the electron density. Our study identifies the ways to increase the efficiency of the PAMP method by maximizing electron density using different means.

Close

PrevNext

View figure in article

• Plasma discharges
• Polarization